数据库问题

Please explain MySQL Joins in simple language(请用简单的语言解释 MySQL Joins)
How can we differ LEFT OUTER JOIN vs Left Join(我们如何区分 LEFT OUTER JOIN 与 Left Join)
MySQL Removing duplicate columns on Left Join, 3 tables(MySQL删除左连接上的重复列,3个表)
MYSQL Left Join how do I select NULL values?(MYSQL Left Join 如何选择 NULL 值?)
joining the same table twice on different columns(在不同的列上两次加入同一个表)
Select distinct records on a join(在连接上选择不同的记录)
Is cross-table indexing possible?(是否可以跨表索引?)
Is inner join the same as equi-join?(内连接与等连接相同吗?)
joining two select statements(加入两个选择语句)
Hierarchical Data in MySQL(MySQL 中的分层数据)
SQL Inner Join On Null Values(空值上的 SQL 内部联接)
mysql structure for comments and comment replies(评论和评论回复的mysql结构)